This invention relates to a method of controlling fuel injection from a fuel injection pump provided in an internal combustion engine, especially a diesel engine, and more particularly to a method of controlling fuel injection from a fuel injection pump in which pilot fuel injection is carried out precedently of main fuel injection.
In the diesel engine, in general, there is produced loud combustion noise due to delayed firing of fuel, particularly markedly when the engine is under a low speed operation or a low load operation.
In reducing such combustion noise, pilot injection (preliminary injection) is known to be effective. The pilot injection is defined as injection of part of the total amount of fuel to be injected which corresponds to an amount of fuel to be consumed in one cycle, precedently of the main injection, whereby the fuel precedently injected undergoes firing to thereby sufficiently increase the temperature of the interior of the engine cylinder. Thereafter, the rest of the fuel is injected (main injection).
Conventionally, Japanese Provisional Patent Publication (Kokai) No. 60-125754 is known to disclose such a fuel injection pump having the above-described function of pilot injection. In this conventional fuel injection pump, a solenoid valve is provided between a high pressure chamber for pressurizing fuel to be pressure delivered to injection nozzles and a low pressure chamber for supplying fuel to the high pressure chamber to control overflow of fuel from the high pressure chamber to the low pressure chamber. The solenoid valve is controlled to selectively open and close during pressurizing and pressure delivery of fuel depending on operating conditions of an engine, whereby the supply of fuel to injection nozzles is intermittently carried out for pilot injection and main injection.
However, in the known fuel injection pump, the time actual firing of fuel injected by pilot injection takes place in the cylinder is detected, and the main injection is started when a predetermined period of time has elapsed from the time actual firing of fuel injected by pilot injection takes place as a reference time. The time of firing of fuel injected by pilot injection can vary due to different states of operation of the engine. Accordingly, the starting time of main injection can vary which is set with reference to the actual firing time of fuel injected by pilot injection. In the meanwhile, the time of termination of the main injection cannot be postponed to a time later than the time determined by the construction of the pumping mechanism including a cam disk for driving of the plunger. That is, according to the method of electronically controlling fuel injection, employed by the known fuel injection pump, if the time of firing of fuel injected by pilot injection is delayed, the time of starting of main injection is delayed accordingly, which results in failure in securing a desired time period of main injection. Consequently, the desired amount of fuel injected through main injection, and accordingly, the desired total amount of fuel injected through pilot injection and main injection cannot be obtained, thus making it impossible for the fuel injection pump having the function of pilot injection to carry out stable fuel injection control.